Researchers on Wednesday cautioned against false hope. The findings suggest that the so-called autism spectrum contains a small but significant group who make big improvements in behavioral therapy for unknown, perhaps biological reasons, but that most children show much smaller gains. Doctors have no way to predict which children will do well.

Researchers have long known that between 1 and 20 percent of children given an autism diagnosis no longer qualify for one a few years or more later. They have suspected that in most cases the diagnosis was mistaken; the rate of autism diagnosis has ballooned over the past two decades, and some research suggests that it has been loosely applied.

The new study should put some of that skepticism to rest.

“This is the first solid science to address this question of possible recovery, and I think it has big implications,” said Sally Ozonoff of the MIND Institute at the University of California, Davis, who was not involved in the research. “I know many of us as would rather have had our tooth pulled than use the word ‘recover,’ it was so unscientific. Now we can use it, though I think we need to stress that it’s rare.”

She and other experts said the findings strongly supported the value of early diagnosis and treatment.

In the study, a team led by Deborah Fein of the University of Connecticut at Storrs recruited 34 people who had been diagnosed before the age of 5 and no longer had any symptoms. They ranged in age from 8 to 21 years old and early in their development were in the higher-than-average range of the autism spectrum. The team conducted extensive testing of its own, including interviews with parents in some cases, to gauge current social and communication skills.

The debate over whether recovery is possible has simmered for decades and peaked in 1987, when the pioneering autism researcher O. Ivar Lovaas reported that 47 percent of children with the diagnosis showed full recovery after undergoing a therapy he had devised. This therapy, a behavioral approach in which increments of learned skills garner small rewards, is the basis for the most effective approach used today; still, many were skeptical and questioned his definition of recovery.

Dr. Fein and her team used standardized, widely used measures and found no differences between the group of 34 formerly diagnosed people and a group of 34 matched control subjects who had never had a diagnosis.

“They no longer qualified for the diagnosis,” said Dr. Fein, whose co-authors include researchers from Queens University in Kingston, Ontario; Children’s Hospital of Philadelphia; the Institute of Living in Hartford; and the Child Mind Institute in New York. “I want to stress to parents that it’s a minority of kids who are able to do this, and no one should think they somehow missed the boat if they don’t get this outcome.”

On measures of social and communication skills, the recovered group scored significantly better than 44 peers who had a diagnosis of high-functioning autism or Asperger’s syndrome.

Dr. Fein emphasized the importance of behavioral therapy. “These people did not just grow out of their autism,” she said. “I have been treating children for 40 years and never seen improvements like this unless therapists and parents put in years of work.”

The team plans further research to learn more about those who are able to recover. No one knows which ingredients or therapies are most effective, if any, or if there are patterns of behavior or biological markers that predict such success.

“Some children who do well become quite independent as adults but have significant anxiety and depression and are sometimes suicidal,” said Dr. Fred Volkmar, the director of the Child Study Center at the Yale University School of Medicine. There are no studies of this group, he said.

That, because of the new study, is about to change.

A version of this article appears in print on , on Page A14 of the New York edition with the headline: Some With Autism Diagnosis Can Overcome Symptoms, Study Finds. Order Reprints | Today’s Paper | Subscribe